The 3rd Generation Partnership Project (3GPP), which is an international standardization organization for the third generation mobile communication system, has proposed a mobile communication system capable of performing emergency-communications between a mobile terminal and an emergency-communication terminal via an IP network (see Non-patent Document 1).
As shown in FIG. 1, such mobile communication system includes an IP network configured of an IMS (IP Multimedia Subsystem) and an IP-CAN (GPRS/I-WLAN).
Here, the IP-CAN is an acronym standing for “IP-Connectivity Access Network,” GPRS is an acronym for “General Packet Radio Service,” and I-WLAN is an acronym standing for “Interworking Wireless Access Network.”
In addition, the IMS is provided with a P-CSCF (Proxy-Call Sever Control Function), an S-CSCF (Serving-Call Server Control Function), an E-CSCF (Emergency-Call Server Control Function), and an HSS (Home Subscriber Server), while the IP-CAN (GPRS/I-WLAN) is provided with a function allowing the forwarding of IP data (SIP signals or VoIP packets).
Here, the S-CSCF, the E-CSCF and the P-CSCF are SIP (Session Initiation Protocol) servers (call control apparatus) for controlling a normal-communication session between a mobile terminal UE and a normal communication terminal or an emergency-communication session between the mobile terminal UE and an emergency-communication terminal (PSAP: Public Safety Answering Point).
Note that, the mobile terminal UE is configured to perform normal communications between the mobile terminal UE and a normal communication terminal (not shown in the drawings) via an S-CSCF#1 (first call control apparatus) and emergency-communications between the mobile terminal UE and the emergency-communication terminal PSAP, via an S-CSCF#2 (second call control apparatus) and an E-CSCF.
By referring to FIG. 2, operations to start emergency-communications between the mobile terminal UE and PSAP in the above-described mobile communication system will be described.
As shown in FIG. 2, in step S7001, the mobile terminal UE transmits, to the P-CSCF, an “Normal Registration Request” for requesting that the S-CSCF#1 perform a normal-communication location registration process (Normal Registration process) for the mobile terminal UE, by using normal-communication user identifiers (IMPI: an IP Multimedia Private Identifier and a Normal IMPU: IP Multimedia Public Identity).
In step S7002, in response to the “Normal Registration Request,” the normal-communication location registration process for the mobile terminal UE is performed between the mobile terminal UE and the S-CSCF#1 by referring to the HSS.
Thereafter, in step S7003, the mobile terminal UE transmits, to the P-CSCF, an “Emergency Registration Request” for requesting that the S-CSCF#2 perform an emergency-communication location registration process (Emergency Registration process) for the mobile terminal UE, by using an emergency-communication user identifier (Emergency IMPU).
In step S7004, in response to the “Emergency Registration Request,” the emergency-communication location registration process for the mobile terminal UE is performed between the mobile terminal UE and the S-CSCF#2 by referring to the HSS.
After the above emergency-communication location registration process is completed, in step S7005, the mobile terminal UE transmits, to the P-CSCF, an “Emergency SIP Invite” for requesting that an emergency-communication session establishment process be performed between the mobile terminal UE and the PSAP, by using the emergency-communication user identifier.
In step S7006, the P-CSCF forwards the received “Emergency SIP Invite” to the E-CSCF.
In step S7007, in response to the “Emergency SIP Invite,” the emergency-communication session establishment process (Emergency Session Establishment process) is performed between the mobile terminal UE and the PSAP.
The mobile terminal UE can perform emergency-communications between the mobile terminal UE and the PSAP by using the emergency-communication session establishment process set as described above.
However, in the above-described mobile communication system, in order to allow emergency-communications from a mobile terminal in which a UICC is not provided (mobile terminal UE of a non-subscribed user), an emergency-communication location registration process, which is required only for performing emergency-communications, has to be performed, in addition to the normal-communication location registration process.
In addition, the above-described mobile communication system requires to perform both of the normal-communication location registration process and the emergency-communication location registration process, since a normal-communication call control apparatus (S-CSCF#1) is different from an emergency-communication call control apparatus (S-CSCF#2) provided to a command station of, for example, police, fire, Japan Coast Guard services or the like.
Examples of the aforementioned example in which a normal-communication call control apparatus (S-CSCF#1) is different from an emergency-communication call control apparatus (S-CSCF#2) includes an example in which a mobile terminal UE performs an emergency-communication session establishment process from a network outside its home network.
Accordingly, in the above-described communication system, even when a normal-communication location registration process for a certain mobile terminal UE is completed, an emergency-communication registration process for the mobile terminal UE has to be additionally performed. Thus, the communication system has a problem that time until starting emergency-communications is longer.    Non-patent Document 1: 3GPP TS23.167 Ver.7.0.0